1. Field of the Invention
This invention relates to a copying device for reproducing an image on a thermally developable photosensitive material.
2. Description of the Prior Art
There have been known various methods for regenerating or copying an image by light. Among these methods, a representative method is a silver halide method. According to this method, a silver halide photosensitive film or photosensitive paper is imagewise exposed to form a latent image, and the resulting latent image is developed with a developing chemical solution and fixed.
Another representative method is an electrophotographic method.
However, these copying processes need exposure, developing and fixing treatments and therefore the treating process is disadvantageously complicated. In addition, the film should be washed with water after treatment since various chemicals are used in the silver halide method.
A novel photosensitive material has been recently developed which does not need any developing treatment by chemicals and fixing treatment. Such photosensitive material is known as Dry Silver Film (trade name, supplied by Minnesota Mining & Manufacturing Co.) and the image recording is effected by a completely dry system, i.e., imagewise exposure, and thermal developing. Thus the film treating process can be simplified. However, in this photosensitive material, various types of material having different photographic characteristics, are not available and therefore, the applicable range is limited. In the field of microfilm, the original is mainly a written document and therefore, it is desirable that the .gamma. value of a photosensitive material is large. Since the above mentioned photosensitive material has only a limited field of application, upon applying the photosensitive material to a microfilm field it is necessary to vary the photographic characteristics of the photosensitive material be changing the developing temperature and time, but it is not possible to make wide changes, and in addition, the treatment is complicated.
There is also a method for improving photographic characteristics by using auxiliary exposure effect, but it is not possible to change, widely, the photographic characteristics.